Dual fueling engine systems with direct and port fuel injectors may be configured to operate under a wide range of engine operating conditions. For example, at higher engine speeds and loads, fuel may be directly injected into engine cylinders to increase engine torque and enhance cooling of cylinder charge mixtures while minimizing chances of engine knock. At lower engine speeds and loads, fuel may be injected via port fuel injection to reduce particulate matter emissions. Specifically, port injected fuel may quickly evaporate as fuel is drawn into an engine cylinder, reducing particulate matter buildup while improving fuel efficiency. Fuel may be injected into an engine via both direct and port fuel injection during mid-speeds and loads in order to improve combustion stability and reduce engine emissions. Therefore, an engine with direct injectors (DI) and port fuel injectors (PFI) can leverage the advantages of each individual injection type.
While it may be beneficial to incorporate port and direct fuel injectors into an engine, supplying fuel via two different injection systems may make it difficult to distinguish injection errors resulting from the port injector from those resulting from the direct injector. One example approach for determining which fuel injection source is introducing fueling errors into the engine is shown by Surnilla et al in US20160131072. Therein, port and direct fuel injector errors are determined by calculating a ratio of a change in fuel multiplier values and a change in fraction of fuel injected into engine via port and direct injection, wherein fuel multiplier values are determined based on a measured air-fuel ratio. A port injector error is determined by calculating a ratio of a change in fuel multiplier values and a change in fraction of port injected fuel, and a direct injector error is determined by calculating a ratio of change in fuel multiplier values and a change in fraction of directly injected fuel.
However the inventors herein have identified potential issues with such a system. As one example, the approach is not able to distinguish fueling errors of direct and port fuel injectors from a common error. As such, an air-fuel ratio error in an engine may have an error contribution from one or more of the direct injector, the port injector, and the common error. The common error may include a common fuel type error and/or an air error. A common fuel type error may occur when a quality of a fuel being injected into the engine degrades. For example, changes in fuel viscosity may cause both port and direct fuel injectors to provide a lower or a larger fuel amount than expected, causing a common fuel type error. Alternatively, a common fuel type error may occur when the actual fuel injected into engine is different from the expected fuel, such as when the oxygen content of a fuel injected into a flex fuel engine deviates from the oxygen content of the fuel refilled into the fuel tank. Further still, the common error may be an air error caused by a degraded engine sensor such as mass air flow sensor, a pressure sensor or a throttle position sensor. Alternatively, an air error in a multi-cylinder engine may occur if some engine cylinders receive more air than other cylinders due to location of the cylinders along an intake air passage or due to a configuration of the intake passage.
Discrepancies in learning air-fuel error in an engine fueled via both direct and port fuel injection may occur when direct and port fuel injector errors are determined without accounting for the common error. For example, a common error in an engine may be misdiagnosed as both a direct and port fuel injector error, with the adaptive fuel multiplier (or transfer functions) for both injectors being affected. As such, this can result in overcompensation for the error. For example, an engine controller may identify the error as a direct injector error or a port injector error and may correct for the error by adjusting a transfer function of the corresponding injector, and disabling the degraded injector. However, if the air-fuel error is due, at least in part, to a common error, the air-fuel error may persist even after the transfer function of a fuel injector is adjusted. In addition, the common error may cause a fuel injector to appear degraded. The controller may disable the fuel injector responsive to the incorrect indication of degradation, as a result of which the advantages of that particular injection type may not be leveraged.
In one example, the issues described above may be addressed by a method comprising: fueling a cylinder via a first and a second fuel injector; estimating each of a first injection error of the first injector, a second injection error of the second injector, and a common error as a function of an air-fuel ratio error and a fraction of fuel injected via each of the first and second injector; and correcting each of the first and second error based on the common error. By separating individual error contributions of each of a direct fuel injector and a port fuel injector from the common error, air-fuel errors may be better compensated for. Overall, engine performance and exhaust emissions are improved.
For example, a total air-fuel error may be determined in an engine fueled with both direct and port fuel injectors as a difference between an actual air-fuel ratio (determined at an exhaust gas sensor) and an expected air-fuel ratio. A portion of that error that is due to a fueling error of the direct fuel injector may be determined as a function of the rate of change in the air-fuel ratio error relative to a rate of change in the fraction of the total fuel injected via direct injection. Likewise, a portion of that error that is due to a fueling error of the port fuel injector may be determined as a function of a rate of change in the air-fuel ratio error relative to a rate of change in the fraction of the total fuel injected via port injection. If the ratios for both the port and direct injectors change by a small magnitude during engine operation but the air-fuel errors corresponding to different engine speed-load conditions are higher than a threshold air-fuel error and have a common directionality (that is, both the port and the direct injector are either indicating a rich air-fuel error or a lean air-fuel error), then a portion of the error may be attributed to the common error. The common error may be learned as a minimum of the two ratios. The controller may then adjust the transfer function of each injector taking into account the common error. For example, the common error contribution may be removed during the transfer function adjustment. As a result, common error may be differentiated from fuel injector errors and accordingly compensated for.
The approach described here may confer several advantages. In particular, the approach allows errors that are common to both fueling systems to be distinguished from fueling errors of individual direct and port fuel injectors. Further, the common errors may be compensated for when adjusting the transfer function of direct and port fuel injectors for their individual errors. By separating individual fueling errors of the direct and port fuel injectors from the common error, air-fuel imbalances generated by overcompensation or under-compensation of fuel injector errors can be reduced. Further, the approach may reduce the erroneous disabling of non-degraded fuel injectors.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.